<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box {
            width: 500px;
            height: 500px;
            border: 5px blue solid;
        }

        .box1,
        .box2,
        .box3,
        .box4 {
            float: left;
            width: 200px;
            /* background-color: red; */
        }

        .box1 {
            height: 150px;
            background-color: black;
        }

        .box2 {
            height: 100px;
            background-color: red;
        }

        .box3 {
            height: 100px;
            background-color: cyan;
        }

        .box4 {
            height: 100px;
            width: 100px;
            /* 若将width设置为200px，又是不同的景象 */
            /* 同行内若有其他元素，就只能往后排，且，若剩余空间不足，则，换行 */
            background-color: blue;
        }
    </style>
</head>

<body>
    <div class="box">
        <div class="box1">1</div>
        <div class="box2">2</div>
        <div class="box3">3</div>
        <div class="box4">4</div>
    </div>
    <script>
        let a = ['2', '3', '1'].map(parseInt)
        console.log(a);
    </script>
</body>

</html>